1. Field of the Invention
The present invention relates to a technical field of an image reading method and an image reading apparatus for photoelectrically reading an original image, particularly, an image photographed on a film.
2. Description of the Related Art
Currently, in case that an image photographed on a photographic film such as a negative film or a reversal film (hereinlater, abbreviated to a film) is printed to a photosensitive material (photographic paper), a direct exposure (an analog exposure) in which the photosensitive material is exposed by projection light of the film, is a main stream.
On the contrary, recently, a printing apparatus using digital exposure, that is, a digital photo printer is put into practical use in which an image photographed on a film is photoelectrically read, and after the read image was converted to a digital signal, the digital signal is subjected to various image processing to obtain image data for recording, and recording the image (latent image) by scan-exposing the photosensitive material to a recording light modulated in correspondence with the image data, to thereby obtain a (finished) print.
In the digital photo printer, an image is converted into digital image data and an exposing condition upon printing can be decided by an image data processing. Therefore, a correcting process for white compression (washed-out highlight) or black compression (dull shadow) in the image due to backlight, photographing using a strobe or the like, a sharpening process, etc. are preferably performed, thereby being capable of obtaining a high quality print that has not been obtained by the conventional direct exposure. Synthesization and division of the image, synthesization of characters, and the like can also be executed by the image data processing and, in response to applications, a freely edited/processed print can be outputted as well.
In addition, according to the digital photo printer, not only an image is outputted as a print (a photograph), but also image data is supplied to a computer or the like or can be stored into a recording medium such as a floppy disk. The image data, thus, can be used for various applications other than a photograph.
A digital photo printer comprises basically a scanner for photoelectrically reading, by an image sensor such as a CCD sensor, an image recorded on a film by allowing to be incident upon reading light to the film and reading the projection light thereof; an image processing device for executing a predetermined image processing for image data read by the scanner or image data supplied from a digital camera or the like and for setting the processed data to image data for image recording, that is, an exposure condition; a printer (image recording device) for recording a latent image, for example, by scan-exposing a photosensitive material by light beam scanning in correspondence with the image data outputted from the image processing device; and a processor (developing device) for developing the photosensitive material exposed by the printer, to thereby obtain a (finishing) print to which the image is reproduced.
In the digital photo printer, in order to output a print to which an image having high quality has been reproduced, it is necessary that as much image information as possible is obtained from a film as an original. A image reading operation with high gradation resolution, therefore, is needed. For this purpose, preferably, the whole density range of the image photographed to the film is read by the maximum use of a dynamic range of a scanner (an image sensor) maximally.
Meanwhile, the whole density range of the image photographed to the film has to be read by the scanner so as to reproduce a proper image. As for an image photographed to a film, however, there is an image that is properly exposed, over-exposed, or under-exposed. An image having an extremely wide density range can be photographed to a film. On the other hand, the dynamic range of the scanner is limited.
That is, in the present circumstances, it is extremely difficult that all images can be read by high gradation resolution under a single reading condition.
In the scanner, thus, prior to an image reading operation (main scan) so as to obtain image data for output, a pre-scan in which an image is roughly read is executed. In correspondence with the image data (pre-scanned data) obtained at the pre-scan, a reading condition of the main scan is set.
Specifically, at the pre-scan time, even if the gradation resolution is low, the whole density range of all images as a target is subjected to an image reading operation under a reading condition in which an output of the image sensor can be accurately read without saturation.
At the main scan time, a reading condition for each image is set from the obtained pre-scanned data so that the output of the image sensor is saturated with slightly lower density than the lowest density of the image and the image reading operation is executed under the reading condition.
Generally, an output signal from the image sensor has low intensity. Accordingly, after the amplification of the output signal by an amplifier, the conversion of the signal by an A/D converter is carried out to thereby obtain a digital image signal.
In the scanner, by this operation, the image reading operation is realized by high gradation resolution in correspondence with images of various densities including an image of over-exposure, under-exposure, and the like by the maximum use of the dynamic range of the scanner.
In the scanner, adjustment of the reading condition is mainly executed by arranging a variable aperture in a reading optical path, adjusting the aperture value (amount), and adjusting (exposure controlling) the light quantity of the reading light incident upon the film. The adjustment of the light quantity by the variable aperture is performed by adjusting the inserting amount of a shading member into the optical path, an aperture amount, and the light quantity that passes through the variable aperture with a shading member such as an aperture plate or the like.
In order to perform preferably a reading operation in correspondence with the images in various states, transporting means of the shading member and control means of the shading member such as an aperture table, which can adjust the inserting amount of the shading member with high resolution and at high precision, are needed. This is one of factors that cause an increase in cost of the scanner.
As one of factors of a decrease in reading precision in the scanner, it is know, what is called, shading in which a light quantity of the light inputted to the image sensor is uneven in a direction of the film surface due to the characteristics of a reading light source or a lens. In the normal scanner, a correction coefficient (shading correction coefficient) for every pixel of the image sensor is calculated. The output signal of each pixel from the image sensor is corrected by the correction coefficient, thereby correcting an error by shading.
However, in the scanner for adjusting the light quantity by the variable aperture, the shading state is varied by the aperture value, that is, the inserting amount of the shading member. Thus, reading precision is decreased in dependence on an aperture value, or in order to stably perform a reading operation at high precision, a shading correction is needed while preparing a plurality of correction coefficients in correspondence with an aperture value, thereby increasing costs of the apparatus.
In order to solve the above-mentioned problems inherent in the conventional technique, an object of the present invention is to provide an image reading method and an image reading apparatus in which when a light quantity is adjusted and a photoelectric reading operation is executed in correspondence with an image state, it is capable of making a variable aperture unnecessary, eliminating a fluctuation of shading, etc., because of the adjustment of light quantity, and realizing a reading operation by the apparatus at low cost and at high precision.
To attain the above object, there is provided an image reading method comprising the steps of: reading photoelectrically an original image by an image sensor; and converting an output signal of the image sensor into a digital signal; characterized in that at least one of an adjusting step of a light quantity which is incident to the image sensor by a light transmittance adjusting operation in an optical path, a sensing condition control step in the image sensor, and an intensity adjusting step of the output signal from the image sensor is used and the maximum value of a signal upon being converted into the digital signal, without recourse to the original image, is set to be constant.
Preferably, the adjusting step of the quantity of the light incident upon the image sensor is performed by allowing at least one of an ND filter assembly with different transmittances, a liquid crystal filter with variable transmittance in accordance with an applied voltage, a liquid crystal display in which a transmittance can be changed in correspondence with the applied voltage, a digital micromirror device, an electrooptical crystal in which the transmittance can be changed in correspondence with the applied voltage, means for adjusting transmission light quantity in correspondence with an angle for a light axis of a plate in which a plurality of mesh plates are arranged in a direction of a film surface under a state where their positions lie on the direction extending in the light axis direction to act on the optical path.
Preferably, the ND filter assembly with different transmittance is at least one of a plurality of ND filters with different transmittances and an ND filter with variable transmittance.
Preferably, the adjusting step of the quantity of the light incident upon the image sensor is performed by allowing at least one of a plurality of ND filters with different transmittances and an ND filter with variable transmittance to act on the optical path.
Preferably, the plurality of ND filters with different transmittances are 5 pieces of glass ND filters in which transmittances are 0.05, 0.1, 0.2, 0.4 and 0.8, and the ND filter with variable transmittance is a meshed ND filter in which the transmittances are 0.05, 0.1, 0.2, 0.4 and 0.8.
Preferably, the image sensor is a CCD sensor and the sensing condition control step is a step of controlling an accumulating time of the CCD sensor.
Preferably, the intensity adjusting step of the output signal from the image sensor is a step of adjusting analog gain for amplifying the output signal from the image sensor.
Preferably, the sensing condition control step of the image sensor is a step of performing different controls among three primary colors so as to absorb a remainder of an adjusting amount of the incident light quantity adjusting step upon the image sensor due to the light transmittance adjusting operation in the optical path.
Preferably, the intensity adjusting step of the output signal from the image sensor is a step of performing different controls among three primary colors so as to absorb a remainder of a control amount of the sensing condition control step of the image sensor.
According to the present invention, there is provided an image reading apparatus, characterized by comprising: an image sensor for photoelectrically reading light carrying an original image; means for controlling a sensing condition of the image sensor; intensity adjusting means for adjusting intensity of an output signal from the image sensor; an analog/digital converter for converting the signal adjusted by the intensity adjusting means into a digital signal; light quantity adjusting means for adjusting a quantity of light incident upon the image sensor by a light transmittance adjusting operation; and setting means for setting a reading condition of the original image so that a maximum value of a signal inputted to the analog/digital converter is constant by at least one of a sensing condition control operation of the image sensor by the sensing condition controlling means, a signal intensity adjustment operation by the intensity adjusting means, and an incident light quantity adjustment operation due to the light transmittance adjusting operation by the light quantity adjusting means, without recourse to the original image.
Preferably, the light quantity adjusting means is at least one of an ND filter assembly with different transmittances, a liquid crystal filter with variable transmittance in accordance with an applied voltage, a liquid crystal display in which a transmittance can be changed in correspondence with the applied voltage, a digital micromirror device, an electrooptical crystal in which the transmittance can be changed in correspondence with the applied voltage, means for adjusting transmission light quantity in correspondence with an angle for a light axis of a plate in which a plurality of mesh plates are arranged in a direction of a film surface under a state where their positions lie on the direction extending in the light axis direction.
Preferably, the ND filter assembly with different transmittance is at least one of a plurality of ND filters with different transmittances and an ND filter with variable transmittance.
Further, according to the present invention, the light quantity adjusting means is preferably at least one of a plurality of ND filters whose transmittances are different and an ND filter whose transmittance is variable.
Preferably, the plurality of ND filters with different transmittances are 5 pieces of glass ND filters in which transmittances are 0.05, 0.1, 0.2, 0.4 and 0.8, and the ND filter with variable transmittance is a meshed ND filter in which the transmittances are 0.05, 0.1, 0.2, 0.4 and 0.8.
Preferably, the image sensor is a CCD sensor, the sensing condition control means is means for controlling an accumulating time of the CCD sensor and the sensing condition control operation is an operation of controlling the accumulating time of the CCD sensor.
Preferably, the intensity adjusting means is an amplifier for amplifying the output signal from the image sensor and the signal intensity adjustment operation is an operation of adjusting analog gain of the amplifier.
Preferably, the reading condition setting means allows the sensing condition controlling means to perform different controls among three primary colors so as to absorb a remainder of an adjusting amount of the incident light quantity upon the image sensor due to the light quantity adjusting means.
Preferably, the reading condition setting means allows the intensity adjusting means to perform different controls among three primary colors so as to absorb a remainder of a control amount of the sensing condition of the image sensor due to the sensing condition controlling means.
With respect to the reading condition setting means, preferably, the following is executed. A main adjustment is executed by transmittance adjustment of the light quantity adjusting means. A range where adjustment cannot be made by the transmittance adjustment of the light quantity adjusting means is subjected to the sensing condition control operation of the image sensor with respect to each of three primary colors. A range where adjustment cannot be further made by the above adjusting operations is subjected to a signal intensity adjustment operation by the intensity adjusting means.